This application claims the benefit of U.S. Provisional Application No. 61/056,284 filed May 27, 2008. The disclosure relates generally to an imaging machine and, more particularly, to the control of toner concentration.
The basic reprographic process used in an electrostatographic printing machine generally involves an initial step of charging a photoconductive member to a substantially uniform potential. The charged surface of the photoconductive member is thereafter exposed to a light image of an original document to selectively dissipate the charge thereon in selected areas irradiated by the light image. This procedure records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document being reproduced. The latent image is then developed by bringing a developer material including toner particles adhering triboelectrically to carrier granules into contact with the latent image. The toner particles are attracted away from the carrier granules to the latent image, forming a toner image on the photoconductive member which is subsequently transferred to a copy sheet. The copy sheet having the toner image thereon is then advanced to a fusing station for permanently affixing the toner image to the copy sheet in image configuration.
In an electrophotographic apparatus, an electrostatic image, formed on the surface of a drum or web, is developed by the application of finely divided toner particles to form a toner image. In certain electrophotographic apparatus, toner images are formed from electrostatic images by brushing a developer mixture of ferromagnetic carrier particles and smaller toner particles across the electrostatic images. The contact of the ferromagnetic particles with the toner particles charges the toner particles by triboelectrification to a polarity needed in order that the toner particles are attracted to the electrostatic images for toning.
In the process of attracting toner particles to electrostatic images for toning, toner particles are depleted from the developer mixture requiring replenishment to avoid a gradual reduction in density of the toner images. Toner replenishment is accomplished by several different types of apparatus. In one type, a given amount of toner is added to the mixture after a given number of copies is made. This approach is acceptable if the amount of toner used for each copy is reasonably predictable. In some apparatus, however, the amount of toner used in any copy or group of copies can vary substantially. For this reason, toner concentration monitors have been designed which automatically add toner according to the results of a monitoring process.
Other examples of analog control are the use of a funnel in the developer apparatus to collect developing material. An inductance coil is wound about the funnel and connected to the motor of a toner dispenser through a bridge circuit. The reactance of the inductance coil varies in accordance to percentage of toner contained in the developing material. Other systems control a toner replenisher by measuring the electric potential of a magnetic developing brush. Still other systems control light reflected from a development brush to measure the concentration of toner in the developer housing. The reflective signal is fed to a computer and the computer determines whether or not the toner could be added and controls a toner replenishment device accordingly. In other approaches to improve toning, often referred to as “Auto-Bias”, the potential of an electrode in the development station is adjusted as a function of the charge density of the electrostatic image.
Other systems control toner dispensers by measuring toner concentration in the developer mixture contained in a developer housing or reservoir, for example, reflecting a light beam from the developer mixture. The measure of the reflectivity of the mixture manifests the proportion of toner to carrier concentration in the mixture. Disadvantages with systems of this type are due in part to “noise” generated in the system, to the fact that the system is only an analog of the amount of toner actually applied to the photoreceptor surface, and to the dependence of the system to the constituents of the developer mixture.
The ratio between the number of toner particles to the number of carrier particles in the developer mixture, i.e. the toner concentration (TC), is a parameter which can change during a production run (unless efficiently controlled) and can contribute to color drift over time. Overall stability of a closed loop TC control system depends on how well the system components are optimized.
To improve overall TC performance, there are at least three major system components that can be optimized; (1) open loop toner replenishment (dispense) and mixing system (i.e., plant itself), (2) a TC measurement system (i.e, sensor), and (3) a closed loop control algorithm.
The present disclosure proposes a state based feedback control algorithm (i.e., a set of instructions) which can be targeted to control the TC in a two-component toner dispense system. A time-delay in the toner dispense can be replaced by states, and each state estimated using the measurement from the TC sensor. States can be defined by creating an open loop state based model of the system. States are estimated from the sensor output using the state estimator. Since each of those states can be controlled as the system evolves over time, we get improved dynamic performance.
The controller does not use an integrator. As a result of not using an integrator in the controller, an anti-windup compensator is not required. System simulation with iGen model, Packer sensor model, and simulated uncertainties is done and compared against prior art methods (i.e., PI controller). Area coverage disturbances, TC sensor drift and sensor noise are injected as uncertainties.